text: Convergent synthesis of a dendrimer begins with what will eventually become the surface of the dendrimer and proceeds inward. The convergent synthetic approach makes use of orthogonal protecting groups (two protecting groups whose deprotection conditions will not remove one another); this is an additional consideration not present when using a divergent approach. The figure below depicts a general scheme for a convergent synthetic approach.
  Convergent synthesis as shown above begins with the dendritic subunit composed of reactive "focal group"  and branched group B (B can be multiply branched in the most generalized scenario, but PAMAMs only split once at each branching point). First,  is orthogonally protected and set aside for further reactions. B is also orthogonally protected, leaving the unprotected  on this molecule to couple with each of the unprotected B groups from the initial compound. This results in a new higher-generation species that is protected on both  and B. Selective deprotection of  yields a new molecule which can again be coupled onto the original monomer, thus forming another new generation. This process can then be repeated to form more and more layers.
  * Note that the black protecting groups for group B represent what will become the outermost layer of the final molecule, and remain attached throughout the synthetic process; their purpose is to guarantee that propagation of dendrimer growth can take place in a controlled fashion by preventing unwanted side reactions.
  * In forming each new layer, the number of B couplings is restricted to two, in sharp contrast to the divergent synthetic approach, which involves exponentially more couplings per layer.
  * Incomplete reaction products (single addition adduct, unreacted starting materials) will have a markedly different molecular weight from the desired product, especially for higher-generation compounds, making purification more straightforward.
  * The reactive focal group  must be terminated onto a final acceptor at some point during the synthetic process; until then, each compound can only be considered a dendron and not a full dendrimer (see page for disambiguation).
  * An advantage to synthesizing dendrons with focal group  as a chemical handle is the ability to attach multiple equivalents of the dendron to a polyfunctional core molecule; changing the core element does not require rebuilding the entire dendrimer. In the case of PAMAM, the focal points of convergently synthesized fragments have been used to create unsymmetrical dendrimers  as well as dendrimers with various core functionalization.
  * Since each successive generation of dendron becomes bulkier, with final attachment to the dendrimer core being the most prohibitive step of all, steric constraints can severely impact yield.